224 Records of the Indian Museion. [Vol. XXII, 



downwards and backwards. These ridges are yellowish in colour 

 and are armed with a simple chitinous plate. The buccal mass 

 is heart-shaped. In front it becomes continuous with the lips of 

 thp mouth, while behind it is produced in two ventral and posterior 

 rounded prominences, between which lie the radular sac below 

 and the oesophagus above. The buccal mass is plentifully supplied 

 with muscles. On cutting through the skin in the middle line of 

 the dorsum of the head and reflecting it outwards, numerous 

 delicate strands of muscle, the protractors, can be seen passing 

 backwards from the sides and dorsum of the skin of the snout to 

 the buccal mass. Below the buccal mass a pair of rather stouter 

 iDands passes downwards and forwards to the skin. These are the 

 depressors. The anterior region of the buccal mass is plentifully 

 supplied with intrinsic muscles, as follows : — 



(i) Superficially and somewhat towards the ventral aspect on 

 each side is a fan-shaped muscle, which arises by a 

 narrow tendon from the lateral region of the ventral 

 aspect and spreads out fan-wise as it passes forwards 

 to be inserted into the oral tube. 



(2) Immediately deep to this is a sphincter muscle, the fibres 



oiiwhich run concentrically around the tube. 



(3) A •mnd of muscle, rather narrower behind than in front, 



arises from the sides of the buccal mass, immediately 

 posterior to the buccal nerve , across which it passes for- 

 wards, spreading out to be inserted round the oral tube. 



Two pairs of strong muscles, the fibres of which are of a 

 shining white colour in contradistinction to the fibres of the 

 preceeding muscles which have a reddish tinge, arise from the 

 main muscle mass of the body and pass forwards to be inserted 

 into the buccal mass. These are the anterior and posterior 

 retractors : — 



(4) The anterior retractors are inserted into the anterior 



ventral aspect of the buccal mass by narrow tendons ; 

 passing backwards side by side they cross the pedal 

 commissure dorsally and can be seen to arise from 

 the main muscle mass near the base of the antennae. 



(5) The posterior retractors arise from the main muscle mass 



and pass forwards and slightly upwards external to the 

 pleuro-pedal commissure of the central nervous system. 

 Here each gives off a slip to the lateral wall of the 

 oesophagus. It then continues forwards internal to the 

 cerebro-pedal commissure and finally joins the side of 

 the buccal mass as a fine tendon which can be traced 

 forwards below the buccal ganglion and ends in a 

 delicate expansion internal and deeply to the muscle 

 (3) noted above. These two muscles are not quite 

 symmetrical for that of the left side arises from the 

 main muscle mass of the body at a higher level than 

 that on the right. 



